A typical outdoor unit has an air-sending chamber accommodating a heat exchanger and an air-sending device and a machine chamber accommodating a compressor and an electric component, and the air-sending chamber is separated from the machine chamber by a partition. In such an outdoor unit, the compressor and the electric component emit heat in the machine chamber. To dissipate heat from the compressor and the electric component, some of such outdoor units include a shell panel in a casing of the outdoor unit having an air inlet through which outdoor air is sucked into the machine chamber (refer to Patent Literature 1, for example).